diff --git a/R/attributes.R b/R/attributes.R
index 1e3348ac6e..7cbcd784c2 100644
--- a/R/attributes.R
+++ b/R/attributes.R
@@ -616,6 +616,31 @@ i_set_vertex_attr <- function(
     igraph_attr_idx_vertex
   )
 
+  # Uniqueness check for vertex "name" attribute
+  if (name == "name") {
+    current_names <- vattrs[["name"]]
+    if (is.null(current_names)) {
+      current_names <- rep_len(NA_character_, vcount(graph))
+    }
+
+    unaffected <- setdiff(seq_along(current_names), index)
+    unaffected_names <- current_names[unaffected]
+
+    if (length(value) == 1 && length(index) > 1) {
+      cli::cli_abort(
+        "Cannot set vertex attribute {.arg {name}} to a single value ({value}) for multiple vertices because it results in duplicate names."
+      )
+    }
+
+    if (any(value %in% unaffected_names)) {
+      dupes <- value[value %in% unaffected_names]
+      cli::cli_abort(
+        "{cli::qty(length(unique(dupes)))} Vertex {?name/names} already {?exists/exist}:
+              {paste(unique(dupes), collapse = ', ')}"
+      )
+    }
+  }
+
   complete <- is_complete_iterator(index)
   name_available <- (name %in% names(vattrs))
   if (!complete && !name_available) {
diff --git a/R/interface.R b/R/interface.R
index e5317fd54e..da03e1b50c 100644
--- a/R/interface.R
+++ b/R/interface.R
@@ -213,7 +213,7 @@ add_vertices <- function(graph, nv, ..., attr = list()) {
   attrs <- append(attrs, attr)
   nam <- names(attrs)
   if (length(attrs) != 0 && (is.null(nam) || any(nam == ""))) {
-    stop("please supply names for attributes")
+    cli::cli_abort("Attribute names must be supplied.")
   }
 
   vertices.orig <- vcount(graph)
diff --git a/tests/testthat/_snaps/attributes.md b/tests/testthat/_snaps/attributes.md
index 172c445888..295eeb44f7 100644
--- a/tests/testthat/_snaps/attributes.md
+++ b/tests/testthat/_snaps/attributes.md
@@ -62,6 +62,22 @@
       Error in `set_graph_attr()`:
       ! `name` must be a single string, not the number 1.
 
+# duplicated vertex names are handled correctly
+
+    Code
+      add_vertices(g, nv = 2, attr = list(name = c("A", "B")))
+    Condition
+      Error in `i_set_vertex_attr()`:
+      ! Vertex names already exist: A, B
+
+---
+
+    Code
+      set_vertex_attr(g, "name", 2:3, "C")
+    Condition
+      Error in `i_set_vertex_attr()`:
+      ! Cannot set vertex attribute `name` to a single value (C) for multiple vertices because it results in duplicate names.
+
 # set_vertex_attrs() works
 
     Code
diff --git a/tests/testthat/test-attributes.R b/tests/testthat/test-attributes.R
index 71d70df15f..684dc40ece 100644
--- a/tests/testthat/test-attributes.R
+++ b/tests/testthat/test-attributes.R
@@ -470,6 +470,19 @@ test_that("good error message when not using character", {
   })
 })
 
+test_that("duplicated vertex names are handled correctly", {
+  g <- make_empty_graph(4)
+  V(g)$name <- LETTERS[1:4]
+  expect_snapshot(error = TRUE, {
+    add_vertices(g, nv = 2, attr = list(name = c("A", "B")))
+  })
+
+  g <- graph_from_literal("A"--"B", "C"--"D")
+  expect_snapshot(error = TRUE, {
+    set_vertex_attr(g, "name", 2:3, "C")
+  })
+})
+
 test_that("set_vertex_attrs() works", {
   g <- make_ring(10)
   g <- set_vertex_attrs(g, color = "blue", size = 10, name = LETTERS[1:10])